I was using 1.5.x version of Mutt and recently upgraded to 1.6.x. When I tried to use tab key to select from my aliases, it wouldn’t work and will show
Query command not defined error.
The solution is simple. According to https://groups.google.com/forum/#!topic/vinux-support/qfaog4LF_PM we only need to unset 2 binds in muttrc.
complete-query #bind editor ^T complete
Then you’ll be able to use tab key again.